Semiconductor integrated circuits which are used in watches, cameras, IC cards and the like are required to be of a packaged construction which is as thin as 0.5 to 2 mm.
An example of a prior art semiconductor device having a thin package construction is shown for example in the Japanese Kokai Publication No. 55-56647. This is a so-called chip-on-board (COB) member in which a semiconductor element such as a semiconductor integrated circuit is directly mounted on a printed circuit board (PCB) formed for example of glass epoxy resin, and metal conductors on the PCB are connected by wire and sealing by epoxy resin or the like is made.
The structure of the prior art semiconductor device of the thin package construction is illustrated in FIG. 1.
In FIG. 1, reference numeral 1 denotes a PCB formed for example of glass epoxy resin. The illustrated PCB is part of a row of PCBs which are connected by a pair of ribbon parts 1A, 1B and pairs of bridging parts 1C and 1D for the respective PCBs 1, as illustrated in FIG. 2.
Such a row of PCBs is formed in the following manner. First, a band-shaped board member S formed for example of glass epoxy is provided, as shown in FIG. 3. A conductive pattern comprising circuit leads 2 and plating leads 5 is formed on the front surface of the board member S, and is connected via throughholes 3 to a terminal pattern 4 formed on the rear surface. The conductive pattern is formed by removing, by means of etching or the like, unnecessary parts of the metal thin film (e.g. of copper) that has been previously stuck to the front surface of the board member S, and applying electroplating of Ni, Au or the like on the surface using the plating leads 5 for conduction of electric current. Thereafter, drilling or other processing techniques are used to form a spot-faced or indented portion (region) 6 for mounting the semiconductor element. Then, stamp-pressing or another method is used to obtain the combination of the row of PCBs 1, the ribbon parts 1A and 1B, and bridging parts 1C and 1D, as shown in FIG. 2.
Plating leads (shown by broken lines) in FIG. 1 are partially removed together with the unnecessary part (which will not become part of the PCBs) of the board member S. At the cut parts 7 of the plating leads at the edge of the PCB 1, a metal thin film which is not covered with any plating layer is exposed.
Then, as shown in FIG. 4, a semiconductor element 8 is bonded by adhesive material to a predetermined position of the spot-faced or indented portion 6 on the PCB 1, and wires 9 are used for connecting the circuit leads 2 with the pads on the semiconductor element 8.
Subsequently, a transfer mold or other means is used for sealing and shaping with a sealing resin 10. During this transfer molding, a die, not shown, is placed over the PCBs and a runner 11 (FIG. 4), which will be described later. Then, press-cutting pressing or the like is used for separating each PCB from the bridging parts and the ribbon parts, to obtain a module. In FIG. 4, the state after the transfer molding and before the subsequent separation into individual modules is shown. The runner 11 and the above described die form the flow path for the sealing resin 10. A gate 12 serving as a flow inlet to the sealing part is also illustrated.
FIG. 5 shows the completed product after the separation into individual units (modules). FIG. 6 and FIG. 7 show sections along line VI--VI, and VII--VII respectively, in FIG. 5. In the figures, 1 denotes the PCB, 2 denotes the circuit lead, 3 denotes the throughhole, 4 denotes the terminal pattern, 5 denotes the plating lead, 6 denotes the spot-faced portion, 7 denotes the plating lead cut part, 8 denotes the semiconductor element, 9 denotes the wire, and 10 denotes the sealing resin. 13 denotes the gate remainder which results after removal of the runner 11 and the gate (see FIGS. 5 and 6) 12.
In the device of the above structure, during the processing of the board member S into the combination as shown in FIG. 2, the metal thin film which is not covered with a plating layer as a protective film, is exposed at the part where the plating lead is cut. Therefore, since the metal thin film is formed of Cu which is easily attacked by corrosive material often present in the environment, the metal thin film becomes corroded or otherwise becomes unsuitable after use over the years.
Moreover, a gate remainder may result in the vicinity of the inlet of the sealing material when the runner and the gate are removed after sealing with resin. Such a gate remainder may cause adverse effects when the device is built in a very thin package of, for instance, a card.